In a recent semiconductor device, application of a Cu (copper) wiring is indispensable for a high-speed operation, low power consumption and others. The Cu wiring is formed by forming a wiring groove in an interlayer insulating film on a semiconductor substrate by using a damascene method, depositing a Cu (copper) film in the wiring groove and on the interlayer insulating film, and then selectively leaving the Cu film in the wiring groove by using a chemical mechanical polishing (CMP) method. As the interlayer insulating film, a silicon oxide film or the like is used.
Since Cu which constitutes the Cu wiring is more easily diffused into an interlayer insulating film such as a silicon oxide film than a wiring material such as Al (aluminum), a bottom surface and a side surface of the Cu wiring are covered with a conductive barrier film such as a TiN (titanium nitride) film. Also, a surface of the Cu wiring is covered with an insulating barrier film together with a surface of the adjacent interlayer insulating film.
In such a Cu wiring structure, Cu ions move along an interface between the interlayer insulating film and the insulating barrier film, so that TDDB (Time Dependence on Dielectric Breakdown) of the Cu wiring occurs. Particularly when a Cu surface is oxidized to CuO after Cu-CMP, Cu is easily ionized and the TDDB deteriorates. For the improvement of TDDB characteristics of the Cu wiring, a technique of subjecting the surfaces of the Cu wiring and the interlayer insulating film to ammonia (NH3) plasma treatment to reduce CuO on the surface of the Cu wiring to Cu, and then forming an insulating barrier film has been known.
As the interlayer insulating film, use of an insulating film having a low dielectric constant, for example, SiCOH has been examined to reduce a capacitance between wirings.
“Effective Cu Surface Pre-treatment for High-reliable 22 nm-node Cu Dual Damascene Interconnects with High Plasma resistant Ultra Low-k Dielectric (k=2.2)” (Non-Patent Document 1) discloses subjecting a Cu wiring formed on an insulating film having a low dielectric constant to ammonia plasma treatment. It also discloses that the ammonia plasma treatment forms a damage layer having a high dielectric constant such as an oxide film on a surface of an interlayer insulating film having a low dielectric constant and RC characteristics and reliability are deteriorated.